[pve-devel] applied: [PATCH storage v2 2/3] zfspoolplugin: check if mounted instead of imported

Thomas Lamprecht t.lamprecht at proxmox.com
Fri Feb 19 15:24:05 CET 2021

On 19.02.21 13:45, Stoiko Ivanov wrote:
> This patch addresses an issue we recently saw on a production machine:
> * after booting a ZFS pool failed to get imported (due to an empty
>   /etc/zfs/zpool.cache)
> * pvestatd/guest-startall eventually tried to import the pool
> * the pool was imported, yet the datasets of the pool remained
>   not mounted
> A bit of debugging showed that `zpool import <poolname>` is not
> atomic, in fact it does fork+exec `mount` with appropriate parameters.
> If an import ran longer than the hardcoded timeout of 15s, it could
> happen that the pool got imported, but the zpool command (and its
> forks) got terminated due to timing out.
> reproducing this is straight-forward by setting (drastic) bw+iops
> limits on a guests' disk (which contains a zpool) - e.g.:
> `qm set 100 -scsi1 wd:vm-100-disk-1,iops_rd=10,iops_rd_max=20,\
> iops_wr=15,iops_wr_max=20,mbps_rd=10,mbps_rd_max=15,mbps_wr=10,\
> mbps_wr_max=15`
> afterwards running `timeout 15 zpool import <poolname>` resulted in
> that situation in the guest on my machine
> The patch changes the check in activate_storage for the ZFSPoolPlugin,
> to check if any dataset below the 'pool' (which can also be a sub-dataset)
> is mounted by parsing /proc/mounts:
> * this is cheaper than running `zfs get` or `zpool list`
> * it catches a properly imported and mounted pool in case the
>   root-dataset has 'canmount' set to off (or noauto), as long
>   as any dataset below is mounted
> After trying to import the pool, we also run `zfs mount -a` (in case
> another check of /proc/mounts fails).
> Potential for regression:
> * running `zfs mount -a` is problematic, if a dataset is manually
>   umounted after booting (without setting 'canmount')
> * a pool without any mounted dataset (no mountpoint property set and
>   only zvols) - will result in repeated calls to `zfs mount -a`
> both of the above seem unlikely and should not occur, if using our
> tooling.
> Signed-off-by: Stoiko Ivanov <s.ivanov at proxmox.com>
> ---
>  PVE/Storage/ZFSPoolPlugin.pm | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)

applied, thanks!

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